Network Working Group J.P. Vasseur, Ed.
Request for Comments: 5073 Cisco Systems, Inc.
Category: Standards Track J.L. Le Roux, Ed.
France Telecom
December 2007
IGP Routing Protocol Extensions forDiscovery of Traffic Engineering Node Capabilities
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
It is highly desired, in several cases, to take into account Traffic
Engineering (TE) node capabilities during Multi Protocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineered
Label Switched Path (TE-LSP) selection, such as, for instance, the
capability to act as a branch Label Switching Router (LSR) of a
Point-To-MultiPoint (P2MP) LSP. This requires advertising these
capabilities within the Interior Gateway Protocol (IGP). For that
purpose, this document specifies Open Shortest Path First (OSPF) and
Intermediate System-Intermediate System (IS-IS) traffic engineering
extensions for the advertisement of control plane and data plane
traffic engineering node capabilities.
Vasseur & Le Roux Standards Track [Page 1]

RFC 5073 IGP Ext for Discovery of TE Node Cap December 2007
signaling. This allows selecting a path that avoids nodes that do
not support a given control plane feature, or triggering a mechanism
to support such nodes on a path. Hence, this facilitates backward
compatibility.
For that purpose, this document specifies IGP (OSPF and IS-IS)
extensions in order to advertise data plane and control plane
capabilities of a node.
A new TLV is defined for OSPF, the TE Node Capability Descriptor TLV,
to be carried within the Router Information LSA ([RFC4970]). A new
sub-TLV is defined for IS-IS, the TE Node Capability Descriptor
sub-TLV, to be carried within the IS-IS Capability TLV ([RFC4971]).
2. Terminology
This document uses terminologies defined in [RFC3031], [RFC3209], and
[RFC4461].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. TE Node Capability Descriptor3.1. Description
LSRs in a network may have distinct control plane and data plane
Traffic Engineering capabilities. The TE Node Capability Descriptor
information defined in this document describes data and control plane
capabilities of an LSR. Such information can be used during path
computation so as to avoid nodes that do not support a given TE
feature either in the control or data plane, or to trigger procedures
to handle these nodes along the path (e.g., trigger LSP hierarchy to
support a legacy transit LSR on a P2MP LSP (see [RFC4875])).
3.2. Required Information
The TE Node Capability Descriptor contains a variable-length set of
bit flags, where each bit corresponds to a given TE node capability.
Vasseur & Le Roux Standards Track [Page 3]

RFC 5073 IGP Ext for Discovery of TE Node Cap December 2007
Five TE Node Capabilities are defined in this document:
- B bit: when set, this flag indicates that the LSR can act
as a branch node on a P2MP LSP (see [RFC4461]);
- E bit: when set, this flag indicates that the LSR can act
as a bud LSR on a P2MP LSP, i.e., an LSR that is both
transit and egress (see [RFC4461]);
- M bit: when set, this flag indicates that the LSR supports
MPLS-TE signaling ([RFC3209]);
- G bit: when set this flag indicates that the LSR supports
GMPLS signaling ([RFC3473]);
- P bit: when set, this flag indicates that the LSR supports
P2MP MPLS-TE signaling ([RFC4875]).
Note that new capability bits may be added in the future if required.
4. TE Node Capability Descriptor TLV Formats4.1. OSPF TE Node Capability Descriptor TLV Format
The OSPF TE Node Capability Descriptor TLV is a variable length TLV
that contains a series of bit flags, where each bit correspond to a
TE node capability. The bit-field MAY be extended with additional
32-bit words if more bit flags need to be assigned. Any unknown bit
flags SHALL be treated as Reserved bits.
The OSPF TE Node Capability Descriptor TLV is carried within an OSPF
Router Information LSA, which is defined in [RFC4970].
The format of the OSPF TE Node Capability Descriptor TLV is the same
as the TLV format used by the Traffic Engineering Extensions to OSPF
[RFC3630]. That is, the TLV is composed of 2 octets for the type, 2
octets specifying the length of the value field, and a value field.
The OSPF TE Node Capability Descriptor TLV has the following format:
TYPE: 5 (see Section 8.1)
LENGTH: Variable (multiple of 4).
VALUE: Array of units of 32 flags numbered from the most
significant bit as bit zero, where each bit represents
a TE node capability.
Vasseur & Le Roux Standards Track [Page 4]

RFC 5073 IGP Ext for Discovery of TE Node Cap December 2007
The following bits are defined:
Bit Capabilities
0 B bit: P2MP Branch Node capability: When set, this indicates
that the LSR can act as a branch node on a P2MP LSP
[RFC4461].
1 E bit: P2MP Bud-LSR capability: When set, this indicates
that the LSR can act as a bud LSR on a P2MP LSP, i.e., an
LSR that is both transit and egress [RFC4461].
2 M bit: If set, this indicates that the LSR supports MPLS-TE
signaling ([RFC3209]).
3 G bit: If set, this indicates that the LSR supports GMPLS
signaling ([RFC3473]).
4 P bit: If set, this indicates that the LSR supports P2MP
MPLS-TE signaling ([RFC4875]).
5-31 Reserved for future assignments by IANA.
Reserved bits MUST be set to zero on transmission, and MUST be
ignored on reception. If the length field is greater than 4,
implying that there are more than 32 bits in the value field, then
any additional bits (i.e., not yet assigned) are reserved.
4.2. IS-IS TE Node Capability Descriptor sub-TLV format
The IS-IS TE Node Capability Descriptor sub-TLV is a variable length
sub-TLV that contains a series of bit flags, where each bit
corresponds to a TE node capability. The bit-field MAY be extended
with additional bytes if more bit flags need to be assigned. Any
unknown bit flags SHALL be treated as Reserved bits.
The IS-IS TE Node Capability Descriptor sub-TLV is carried within an
IS-IS CAPABILITY TLV, which is defined in [RFC4971].
The format of the IS-IS TE Node Capability sub-TLV is the same as the
sub-TLV format used by the Traffic Engineering Extensions to IS-IS
[RFC3784]. That is, the sub-TLV is composed of 1 octet for the type,
1 octet specifying the length of the value field.
The IS-IS TE Node Capability Descriptor sub-TLV has the following
format:
TYPE: 1 (see Section 8.2)
LENGTH: Variable
VALUE: Array of units of 8 flags numbered from the most
significant bit as bit zero, where each bit represents
a TE node capability.
Vasseur & Le Roux Standards Track [Page 5]

RFC 5073 IGP Ext for Discovery of TE Node Cap December 2007
The following bits are defined:
Bit Capabilities
0 B bit: P2MP Branch Node capability: When set, this indicates
that the LSR can act as a branch node on a P2MP LSP
[RFC4461].
1 E bit: P2MP Bud-LSR capability: When set, this indicates
that the LSR can act as a bud LSR on a P2MP LSP, i.e., an
LSR that is both transit and egress [RFC4461].
2 M bit: If set, this indicates that the LSR supports MPLS-TE
signaling ([RFC3209]).
3 G bit: If set, this indicates that the LSR supports GMPLS
signaling ([RFC3473]).
4 P bit: If set, this indicates that the LSR supports P2MP
MPLS-TE signaling ([RFC4875]).
5-7 Reserved for future assignments by IANA.
Reserved bits MUST be set to zero on transmission, and MUST be
ignored on reception. If the length field is great than 1, implying
that there are more than 8 bits in the value field, then any
additional bits (i.e., not yet assigned) are reserved.
5. Elements of Procedure5.1. OSPF
The TE Node Capability Descriptor TLV is advertised, within an OSPFv2
Router Information LSA (Opaque type of 4 and Opaque ID of 0) or an
OSPFv3 Router Information LSA (function code of 12), which are
defined in [RFC4970]. As such, elements of procedure are inherited
from those defined in [RFC2328], [RFC2740], and [RFC4970].
The TE Node Capability Descriptor TLV advertises capabilities that
may be taken into account as constraints during path selection.
Hence, its flooding scope is area-local, and it MUST be carried
within an OSPFv2 type 10 Router Information LSA (as defined in
[RFC2370]) or an OSPFv3 Router Information LSA with the S1 bit set
and the S2 bit cleared (as defined in [RFC2740]).
A router MUST originate a new OSPF Router Information LSA whenever
the content of the TE Node Capability Descriptor TLV changes or
whenever required by the regular OSPF procedure (LSA refresh (every
LSRefreshTime)).
Vasseur & Le Roux Standards Track [Page 6]

RFC 5073 IGP Ext for Discovery of TE Node Cap December 2007
The TE Node Capability Descriptor TLV is OPTIONAL and MUST NOT appear
more than once in an OSPF Router Information LSA. If a TE Node
Capability Descriptor TLV appears more than once in an OSPF Router
Information LSA, only the first occurrence MUST be processed and
others MUST be ignored.
When an OSPF Router Information LSA does not contain any TE Node
Capability Descriptor TLV, this means that the TE node capabilities
of that LSR are unknown.
Note that a change in any of these capabilities MAY trigger
Constrained Shortest Path First (CSPF) computation, but MUST NOT
trigger normal SPF computation.
Note also that TE node capabilities are expected to be fairly static.
They may change as the result of configuration change or software
upgrade. This is expected not to appear more than once a day.
5.2. IS-IS
The TE Node Capability sub-TLV is carried within an IS-IS CAPABILITY
TLV defined in [RFC4971]. As such, elements of procedure are
inherited from those defined in [RFC4971].
The TE Node Capability Descriptor sub-TLV advertises capabilities
that may be taken into account as constraints during path selection.
Hence, its flooding is area-local, and it MUST be carried within an
IS-IS CAPABILITY TLV having the S flag cleared.
An IS-IS router MUST originate a new IS-IS LSP whenever the content
of any of the TE Node Capability sub-TLV changes or whenever required
by the regular IS-IS procedure (LSP refresh).
The TE Node Capability Descriptor sub-TLV is OPTIONAL and MUST NOT
appear more than once in an ISIS Router Capability TLV.
When an IS-IS LSP does not contain any TE Node Capability Descriptor
sub-TLV, this means that the TE node capabilities of that LSR are
unknown.
Note that a change in any of these capabilities MAY trigger CSPF
computation, but MUST NOT trigger normal SPF computation.
Note also that TE node capabilities are expected to be fairly static.
They may change as the result of configuration change, or software
upgrade. This is expected not to appear more than once a day.
Vasseur & Le Roux Standards Track [Page 7]

RFC 5073 IGP Ext for Discovery of TE Node Cap December 20076. Backward Compatibility
The TE Node Capability Descriptor TLVs defined in this document do
not introduce any interoperability issues. For OSPF, a router not
supporting the TE Node Capability Descriptor TLV will just silently
ignore the TLV, as specified in [RFC4970]. For IS-IS, a router not
supporting the TE Node Capability Descriptor sub-TLV will just
silently ignore the sub-TLV, as specified in [RFC4971].
When the TE Node Capability Descriptor TLV is absent, this means that
the TE Capabilities of that LSR are unknown.
The absence of a word of capability flags in OSPF or an octet of
capability flags in IS-IS means that these capabilities are unknown.
7. Security Considerations
This document specifies the content of the TE Node Capability
Descriptor TLV in IS-IS and OSPF to be used for (G)MPLS-TE path
computation. As this TLV is not used for SPF computation or normal
routing, the extensions specified here have no direct effect on IP
routing. Tampering with this TLV may have an effect on Traffic
Engineering computation. Mechanisms defined to secure IS-IS Link
State PDUs [RFC3567], OSPF LSAs [RFC2154], and their TLVs can be used
to secure this TLV as well.
8. IANA Considerations8.1. OSPF TLV
[RFC4970] defines a new codepoint registry for TLVs carried in the
Router Information LSA defined in [RFC4970].
IANA has made a new codepoint assignment from that registry for the
TE Node Capability Descriptor TLV defined in this document and
carried within the Router Information LSA. The value is 5. See
Section 4.1 of this document.
8.2. ISIS sub-TLV
IANA has defined a registry for sub-TLVs of the IS-IS CAPABILITY TLV
defined in [RFC4971].
IANA has made a new codepoint assignment from that registry for the
TE Node Capability Descriptor sub-TLV defined in this document, and
carried within the ISIS CAPABILITY TLV. The value is 1. See Section4.2 of this document.
Vasseur & Le Roux Standards Track [Page 8]

RFC 5073 IGP Ext for Discovery of TE Node Cap December 20078.3. Capability Registry
IANA has created a new registry to manage the space of capability bit
flags carried within the OSPF and ISIS TE Node Capability Descriptor.
A single registry must be defined for both protocols. A new base
registry has been created to cover IGP-TE registries that apply to
both OSPF and IS-IS, and the new registry requested by this document
is a sub-registry of this new base registry.
Bits in the new registry should be numbered in the usual IETF
notation, starting with the most significant bit as bit zero.
New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities:
- Bit number
- Defining RFC
- Name of bit
IANA has made assignments for the five TE node capabilities defined
in this document (see Sections 8.1 and 8.2) using the following
values:
Bit No. Name Reference
--------+---------------------------------------+---------------
0 B bit: P2MP Branch LSR capability [RFC5073]
1 E bit: P2MP Bud LSR capability [RFC5073]
2 M bit: MPLS-TE support [RFC5073]
3 G bit: GMPLS support [RFC5073]
4 P bit: P2MP RSVP-TE support [RFC5073]
5-7 Unassigned [RFC5073]
9. Acknowledgments
We would like to thank Benoit Fondeviole, Adrian Farrel, Dimitri
Papadimitriou, Acee Lindem, and David Ward for their useful comments
and suggestions.
We would also like to thank authors of [RFC4420] and [RFC4970] by
which some text of this document has been inspired.
Adrian Farrel prepared the final version of this document for
submission to the IESG.
Vasseur & Le Roux Standards Track [Page 9]

RFC 5073 IGP Ext for Discovery of TE Node Cap December 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Vasseur & Le Roux Standards Track [Page 13]